Electrical apparatus for detecting unbalance in rotating bodies



J. O. MESA ELECTRICAL APPARATUS FOR DETECTING Nov. 4, 1952 UNBALANCE: 1N ROTATING BODIES 2 SHEETS-Smm 1 Filed Jan. 4, 1945 l ll w WN m Nov. 4, 1952 J. o. MESA ELECTRICAL APPARATUS FOR DETECTING UNBALANCE IN ROTATING BODIES 2 srEETS-sx-IEET 2 Filed Jan. 4, 1945 l -Jz l /yo J5 Ir A M92/ l/ Jya mgl/Jar?.

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22 .W i l, I a .x HV1 6 m Y L@ AM I|\INQ if H II U HA IIIWI |l|| VL E MT P Patented Nov. 4, 1952 ELECTRICAL APPARATUS 'FOR `VDE'IECTING UNBALANCE IN ROTATING BODIES Joseph 0. Mesa, Winnetka, Ill., assignor to Stewart-Warner Corporation, '.Chicago, .-Ill., .La corporationof Virginia Application January 4, 1945, Serial No. 571,307

(Cl.l 'Z3-66) l 14 Claims.

The present 'invention `relates to balancing and more particularlyto anew `and improved method of and apparatus for `checking the balance of and for balancing rotating bodies.

In .the past Imanydifferent methods of and apparatus for balancing have been developed and used with varying degrees of success. In one known -arrangementthe locus `of unbalance is determined at the resonance frequency ofthe system. The system may comprise, for example, an elastic damped-vibrational system like alfreely rotating automobile or airplane wheel which is preferably brought up to a speed above. the resonantnspeedand then. allowed freely to decelerate to thefresonantfspeed at Vwhich acheck of the unbalanceis made. It is known that at the resonant frequency the amplitudeof the resulting vibrations or displacement is` a vmaximurnas is 'the velocity of the vibrationV or displacement. It is known further that at' this Vspeed thevelocity is. in phase with .the force of unbalance, i. e., with the locus `of unbalance, .andthatthedisplacementV lags .the velocity .by .90 degrees.

The best of the .:prior.art fbalancing systems includecircuits andthe like for lflashing .a .stroboscopic light. source, :such as a gaseous discharge tube, .in synchronism with vthe .vibrations and correlating .the flashing with ;the. rotating body toldetermineV the locusof theunbalance. .In certain of `thepprioixart.arrangements, the tube' is flashed.- at. the moment thevelocity` ofithe vibration :or .displacement is .the greatest. This -is accomplished v,by vvelocity responsive .means (which :may .be .a yvoltage generator, such.. as va pick-.up coil) .actuated by .the'vibrational .displacement of the rotating system .either .in;a radialor axial. direction, vdepending upon whether the Vstatic l.and .dynamic balance to be checked. If the-voltage generator is arranged to .be responsive to vertical upward displacement of the: rotating body and the light flashes occur at the time .when the vibration velocity is? at. its instantaneousmaximuml value, :the rotating body will appear stationary.in;the position;at .which the force .is-'a maximumupward. If then the wheel isbrought toirestwith the wheel its; apparent stationaryposition, the locus of unbalance will be at thetop ,and a .weight can be added to the rotating body at the bottom to opposexand to neutralize theforce of unbalance.

Infthe velocity responsive arrangementsof the prior art, trouble has been encountered in correlating theflashing or ring ofxthe stroboscopic light sourcewith thelocusof unbalance, i. e., with phasing, .under widely/varying conditionsof amplitude and resonant velocity. In some arrangementstrouble occurs athigher angular or resonant velocities, whereas in other arrangements the-.diicultyappears at low amplitudes. Just what causes the trouble is not known, `but it'may:.result from the intricacyof the integrating, amplifying, limiting .and differentiating operations whichare performedk by the balancing apparatus.

.Ther primaryobject .of the Apresent invention is to provide .anew` and improvedfmethod of ,and apparatus for balancing rotating fbodies.

. Anothergobject of the present, invention isto provide=a new r.and,.improved'method of-.and apparatus for` balancing vrotating bodies which is simple to practice, in construction, and which provides the vproper phase of firing, or flashing of the. light. source under widely varying conditions of amplitude; and resonant velocity ofthe rotating'bOdy.

.Another .object ofthe present linventionA is .to provide anew` and improved method of .balancing rotatingbodies which comprises the step. of flashingtthelightvsource in response: to displacement and when the vibrational displacement is-substantially zero.

.Another objectof theppresentinvention is to provide::new and improved balancing1 apparatus which includesalight source and displacement responsive means for flashing the light source, and,.more specifically, flashing the light source at substantially the moment thevibrational displacement is;zero and-.preferably, taking place in a .particular `direction.

Another. object; of fthe; present invention .is to provide. a; new and improved balancing apparatus which ncludeszayminimum of electrical means and l.which includes,gon.the other hand, mechanicalrmeans for-amplifying vthe vibration and for producingl flashing impulses at substantially the time the-vibrational displacement is zero.

, Another .object of the present y. invention is to provide :a new and limproved balancing apparatus including mechanical. means forV amplifying ,the vibrationalrdisplacement. .and4 for producing electrical.controlfimpulsesfat the moment the displacement is substantiallyzero.

Another object.. of the present invention is to provide a new and improved'simpliiiedbalancing apparatus insuring ,=properv phasev of firing of the light source1underlvarying conditions of amplitude and.: resonantv velocity, Y as Well` as providing amplitude and frequencymeasurements whereby the balancing operation .may `be made .more effectively andfsatisfactorily.

A more specic object of the present invention is to provide new and improved balancing apparatus of the character aforesaid which includes but three electron tubes, namely, a gaseous discharge device which is fired synchronously with the zero displacement of the vibrating system, a second tube utilized for indicating the frequency of the vibrations, and a third tube for providing an indication of the amplitude.

Other objects and advantages of the present invention will become apparent from the ensuing description, in the course of which reference is had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of an embodiment of the present invention adapted to be supplied with power from an alternating current source;

Fig. 2 is a similar representation ofanother embodiment of the present invention adapted to be energized from a direct current source;

Fig. 3 is a view illustrating the adjustable mounting of a pair of electrical contacts forming part of the mechanical impulse producing means employed in the arrangements of Figs. 1 and 2;

Fig. 4 is a graph illustrating the nature of the vibrational velocity of a rotating body;

Fig. 5 is a graph illustrating the vibrational displacement of the body;

Fig. 6 is a graph illustrating, on a reduced scale, a resultant modied Vibrational displacement from which it may be noted that the wave shape is mcdied by limiting the amplitude and that a substantial velocity occurs only substantially at the point -of zero displacement of the rotating body;

Fig. 7 is a graph illustrating the nature of the control impulses produced as a result of the. displacement of the character depicted in Fig. 6;

Fig. 8 is a graph which will be referred to in the description of the measurement of amplitudes of vibrations, the curve illustrating vibrations of two somewhat different amplitudes; and

Fig. 9 is a graph showing how the magnitude and phase angle of the vibrational velocity vary with frequency.

The embodiment of the invention illustrated in Fig. 1 will rst be described. It may be mentioned that the primary distinction between it and the embodiment of Fig. 2 resides in the fact that the apparatus of the former is energized from an alternating current source and that of the latter from a direct current source.

The apparatus of Fig. 1 includes, in the main, a power pack i@ for supplying direct current from an alternating current source; means indicated generally by the reference character i2 including a tube ifi for producing periodic light ashes (hereinafter called, for convenience, a flasher circuit); means indicated generally by reference character i6 including a second tube i8 for indicating the frequency of the vibrations and, therefore, the rotational frequency of the rotating apparatus being balanced (hereinafter called a frequency circuit) and means indicated generally by reference character 2@ including a third tube 22 for providing an indication of the amplitude of the vibrations (hereinafter called the amplitude circuit) The various tubes are controlled, in accordance with one of the primary features of the present invention, by mechanical vibration amplifying and impulse producing means of which two are preferably employed, as indicated generally by the reference characters 2d and 26, and

d both of which are simultaneously operated in response to the displacement of the rotating body.

The power pack it is supplied with alternating current from a suitable source (not shown) to which the primary winding 3@ of a transformer 32 may be connected. The transformer includes three secondary windings 36, SS and 38, the first of which supplies anode potential to the anodes it of a rectifier tube i2 (which may be of the 5W4G tube), the second of which supplies heater current to the iilamentary type cathode @d of the tube, and the third of which supplies cathode heater current to tubes i4, i3 and 22. The midpoint'I of secondary winding 34% is connected to ground conductor it which thus forms the negative direct current power line while the positive direct current power line i3 is connected to the cathode le through a lter of known type which may include a choke coil 5t and a condenser 52 (having a value of about 20 microfarads). The choke coil is in series with line 48 and the condenser is connected across the positive and negative power supply lines.

The flasher and frequency circuits l2 and I6 are connected to the positive power supply line (i8 through a filter coil 54 connecting the line to a branch supply line 5G. A lter condenser 51 is connected across conductors 56 and et. In similar manner the amplitude circuit 2t is connected to the positive supply line through a filter coil 58 connecting the supply line t0 a branch supply line tu, and a iilter condenser 6l is connected across conductors 6@ and lit. The described power supply circuit arrangement decreases the possibility of interference between the circuits.

The flasher and frequency circuits are controlled in response to the vibrational displacement of the rotating body. More specifically, the circuits are supplied with control impulses in response to vibrational displacement and at a time when this displacement is substantially zero. These impulses are arranged to flash or re tube lli when the vibrational displacement is substantially zero, and tube Hi is thus used as a stroboscopic light source. It is also used to control the frequency circuit. Te tube Hi may be fired either upon or the closure or opening of a, mechanical switch, but it is preferred, and the arrangement has been illustrated as being of a type wherein firing occurs when contacts are opened.

The means 2d responsive to displacement, which of itself forms another feature of the invention, constitutes also movement amplifying and amplitude limiting means. It includes a pair of stationary contacts 62 and M illustrated diagrammatically in Fig. 1 and in greater detail in Fig. 3. The contacts are made of very exible wires and preferably made of Phosphor bronze wire. The means includes also a movable contact @t secured to the united ends of a pair of resilient and relatively long spring arms 68 and iii. The spring arms may be constituted of Phosphor bronze reeds having a thickness of about ve thousandthsinch. The contact 66 may have a thickness of about one-eighth inch and the spacing between it andthe stationary contacts should be about a few thousandths (about three thousandths inch) on each side when it is centered. The arm l@ is secured to a fixed support such as that illustrated diagrammatically by reference character 'H and the united contact carrying ends 66 are disposed substantially between the contacts 62 and 64.

The movable Contact 66 is vibrated between the limits defined by the two substantially stationary contacts 62 and 64 in response to vibrations of the rotating body, which, for convenience, will hereinafter be considered to be an automobile wheel. in checking the unbalance, the wheel is preferably suspended above ground for free rotation by some suitable device. The vibrations of the wheel (which may be the radial or axial vibrations, depending upon whether the wheel is to be balanced statically or dynamically) are transmitted to the arms 00 and 10 and thus to the movable contact 65. Assuming that the Wheel is to be balanced statically, then the radial movements of the wheel'support, preferably the Vertical radial movements, are utilized to move the movable contact 00. These movements are transmitted to the contact through the reeds 80 and 10, which are connected to the wheel support (the axle, usually) by a small permanent'magnet 'I2 secured to the free end of reed S3. As the wheeland its support move vertically, the magnet '|2 is moved vertically to oscillate contact 66 a limited distance between the stationary contacts E2 and 64. The wheel support vibrates through a considerably greater distance than that between contacts 62 and 04 although the displacement is amplified because of the length of the reeds. Thus the movable contact quickly moves between contacts, and impulses are produced whenever the movable contact opens a circuit controlled thereby. The resonance frequency cf the switch assembly should be high as compared with the working range of frequencies, i. e., the frequencies ordinarily encountered in systems of the character b-eing balanced. The generally Gothic-like arrangement of the reeds |58 and '10 has been found to contribute to the satisfactory operation of the arrangement, although other arrangements may be used.

In order to insure ring of the tube I4 at substantially rero displacement, the movable contact 6% has to be centered with respect to contacts S2 and G4. rhis is accomplished by some suitable adjustable contact supporting means, such as that illustrated in Fig. 3. Referring to this gure, it will be seen that the two stationary contacts 02 and S4 are mounted upon supporting blocks 'I4 and l0, respectively, and that these are mounted upon a plate 'I8 sldably secured to a main supporting plate t0. The contact supporting block i4 is individually adjustably mounted on sliding plate 'I3 to vary the spacing between the stationary contacts. The adjustment is effected by suitable means, such as a rotatable adjusting screw 82.

The two contacts are movable simultaneously by movement of the sliding plate i8 as by an adjusting screw 84. Thus when the screw 04 is rotated, the two contacts are moved simultaneously so that the movable contact may be centered relative to them. The manner in which the centering is effected in checking the unbalance will be hereinafter described in greater detail.

1t may be well to mention at this point that while the described switch assembly includes two stationary contacts which are alternately engaged by the movable contact, only one of these contacts (contact E2) is used during the balancing operation. The other contact 64 is utilized in centering the movable contact and it is arranged to be cut out from the flasher circuit during the balancing operation by means of a manually operable switch 86.

"Theitube I4 is'fired-eachitimet'he movable contact moves vout of .engagement with a stationary contact. When'the switch 186' is closed, the tube is red twice per cycle and, to center the movable contact, the stationary contacts are moved relative to the movable contact by means of screw-84 until the tube fires sothatthe apparent positions of the wheel are 180 degrees apart. When thus adjusted, the movable contact is properlycenteredrelative tothe stationary contacts.

The tube I4 is preferably` fired Ybythe application of a positive voltage impulse to 4thetcontrcl grid of the tube. The tube maybe offthe 631131 type. The cathode of the-tube is connected to the negative supply linel 46 through a cathode bias resistor 92 v(of about 2000 ohms). Theshield grid 94'is connected to the cathode through '-a resistor 9E (of about .1 megohm). LIhe anode 98 of the'tube is connected-to the branch supply-line 5B through the series connected resistors |00 (of about 6000 ohms) and |02 (ofabout 4000 ohms), of which the latter and its-associated shunt condenser |04 (of about 1000 mf.) form an essential part of the frequency circuit I6.

The tube I4 is coupled to the switch'assembly through a coupling condenser |06 (of `about L08 mi), one plate of which is connected to grid 88 by conductor |08, and the other of which is connected by conductor |0 to the junction of a pair of potential dividing resistors ||2 and||4 (each of about .5 megohm) connected in series across conductors 56 and 46. The'junctionof the two resistors is connected to contacts 02 'and '64 through conductor |6 (having a normally closed amplitude centering control switch I interposed therein) and through conductor ||8 and switch 86, respectively. When the movable contact engages either of the fixed contacts, the resistor ||4 is shortedand the plate 0f condenser |05 remote from grid is connected to ground through reed 10 and ground connection |20.

The grid of tube I4 is rendered more positive and the tube rires whenever the movable contact 66 moves out of engagement with a stationary contact. When in engagement with 4a stationary contact, the condenser |00 is charged-to a relatively low potential through resistor |22 (of about 1 megohm) connecting the grid to the junction of resistors |24 and |20` (of about 8000 ohms and 20,000 ohms, respectively) forming a potential divider connected across conductor 55 and ground conductor 46 through a third resistor |28 (of about 400 ohms). It may be noted, therefore, that when the movable contact is in engagement, say with contact 62, one plate of condenser |00` is connected to ground and the other to the junction of the potential dividing resistors |24 and |26. When the movable contact is disengaged from the stationary contact, a positive voltage impulse is applied to the grid 88 Vof tube I4 through the coupling condenser |06, the normally grounded end of which is substantially raised to a much higher potential by breaking of the ground connection' and leaving it effectively connected across the voltage dividingresistor 4.

When the tube I4 is rendered conductive, a current impulse is caused to flow throughit to lower the anode voltage belowthe ionization potential and to bias its .grid negatively thereby to render the tube nonconductive. The current impulse is supplied by a condenser |30 (of about 2 mf.) which is normally charged and which is connected directly across the anode fandcathode of the tube. The condenser dischargelthrough 7 the tube lowers the anode-cathode voltage and applies a negative bias to the grid because of the increased voltage drop across the cathode biasing resistor 92.

During the time that the movable contact is between the two stationary contacts, the condenser |06 is charged to a new and relatively low potential dependent upon the voltages at the junctions of resistors ||2 and lie and resistors |24 and |26. When the movable contact 6 engages the other stationary contact, resistor H4 is again short-circuited. This suddenly lowers the potential of the ground end of condenser it and results in the application of a voltage impulse on grid 88. This impulse, however, is of such polarity and magnitude (it is negative and roughly about half of the other impulse) as not to eifect firing of the stroboscopic tube. Thereafter, the condenser Hit is again recharged to its original potential.

The vibration frequency is obtained by measuring the average value of the current flow through the tube i8 (which may be a diode of the 6X5 type) which is dependent upon the frequency with which tube It is fired. Cathode |32 of tube I8 is connected by conductor 35 to the junction of resistors and it?. Its anode |33 is connected to the junction of resistors and |28 through a meter its which may be a sensitive ammeter. rThe voltage of the anode of the diode is very nearly that of line '5t while the cathode voltage is dependent on the voltage drop across resistor |02 and the average charge of condenser |04 which is connected parallel to resistor |02. The ow of current through resistor |92 is dependent upon the frequency of the rlring of the tube I4 with the result that the meter |410 provides a reading proportional to the frequency. Each time the tube |l| hashes the condenser i3@ first discharges through the tube and is then charged through the series connected resistors |00 and EQ2. The charging current causes a voltage drop across resistor it? which is utilized to charge condenser |06. The potential of the cathode |34 of diode i8 falls below that of its anode and current thus flows through the diode and meter |40. rlhe time constant of the frequency circuit is chosen to be relatively long so that the average potential of the diode cathode and the average value of the diode current depend upon the interval between iiashes of tube lil. The meter reading, therefore, is a function of the flashing' frequency and is independent of the amplitude of the vibrations.

The amplitude circuit is so constructed and arranged that a meter id in circuit with tube 22 provides a reading of the amplitude which is independent of the vibration frequency. The arrangement is such that the tube E2 is periodically rendered conductive in synchronism with the vibrations and preferably twice for each revolution of the wheel. Each time it is rendered conductive, a current impulse flows through the tube and meter. The current impulse has a value dependent upon the amplitude. In the instant embodiment, the current impulse varies inversely with the velocity of the vibration, which, it will be shown shortly, varies proportionately with the amplitude of the vibration so 'that the meter thus provides an indication of the amplitude of the vibrations.

The tube 22 is a pentode (preferably of the 6SJ7 type) having a substantially constant current flow characteristic. The tube is biased to cut-offy when the movable contact |44 is in ensagement with either of the stationary contacts |46 and |48 of the control means 26, which is identical with device 24, except that it has no manually operable switch for cutting out one of the contacts, and which is operatively connected to the wheel support by the same magnet lf2 referred to in the description of device 24. When the movable contact I 44 is between the stationary contacts, the tube 22 is rendered conductive for a length of time depending on the time it takes for the movable contact to move between the two stationary contacts.

The control means 26 is coupled to the control grid |50 of tube 22 through resistor |52 (of about .1 megohm), a normally closed centering switch |53, and branch conductors |54 and |56 leading to the stationary contacts. The cathode |53 of the tube is connected to a bias resistor |60 (of about 1000 ohms) through a conductor |62. A grid leak resistor |64 (of about .1 megolim) is connected across the cathode and the contactor end of resistor I 52.

The cathode bias resistor |60 is connected across the positive branch supply conductor G and ground conductor 46 through the series connected voltage dividing resistors |66 and |68 (of about 7500 and 10,000 ohms, respectively). The screen grids |10 of tube 22 is connected to the junction of resistors |56 and |68, of which the former is shunted by a by-pass condenser |`l2 (of about 20 mi). The suppressor grid llt is connected to the cathode |58.

The switch assembly controls the bias voltage applied to grid |50. When open, the grid bias is reduced to Zero and when closed the grid is biased negatively to cut-oir by the voltage drop across resistor |60, the grid being connected to the ground end of the resistor by conductor et, conductor |73, the switch assembly and resistor |52.

The amplitude meter M2 is connected between the plate Ii of tube 22 and conductor 65 through resistors |89 and |82 (of about .2 megohm and i500 ohms, respectively). To reduce the pulsations of the meter, a condenser Hit (of about 4 mf.) is connected across the series connected meter and resistor |80.

The switch assembly of control means 2t is preferably centered by connecting it to the flasher circuit i2 so that the centering may be effected in the same manner as the centering of control means 2li. When it is desired to center the control means 2'5 the previously referred to switches lil and |53 are operated, preferably simultaneously, so that the stationary contacts IS and Hi8 are coupled to flasher tube |4 through a circuit including the previously referred to switches ||7 and |53 and conductor |86. If desired, the switches ||l and |53 may be mechanically interconnected for simultaneous operation.

Before proceeding with a description of the operation of the device in connection with the checking and balancing of a rotating body such as an automobile wheel, it is deemed best to consider briey Figs. 4 to 9, inclusive, in order that a more comprehensive understanding may be had ofthe principles underlying the present invention.

Eig. 4 depicts graphically the vibrational veloc1ty of the rotating body. From this it may be noted that the velocity varies sinusoidally, and from Fig. 9 it may be noted that when the system 1s rotating at resonant frequency, the velocity is a maximum and the phase angle between the velocity and force on one hand and locus of balance on the other is Zero.

The vibrational displacement is depicted in Fig.

and from this-it may be noted that it is equivalent to the time integral of the curve of Fig. 4.

Fig. 6 depicts the displacement of the movable contact 55 which is mounted at the ends of the reeds 6B and l0 and which is moved in synchronism with the vibrations of the rotating body. rhe vibrations are amplied by the mechanical amplifier constituted by the lever arm of the reeds, and the amplined vibrations are limited by the stationary contacts S2 and 64. When the movable contact is properly centered, the movable contact moves quickly with an increased velocity from one to the other of the stationary contacts at the time of zero displacement or at the time the velocity is a maximum.

Fig. '7 depicts the nature oi the control impulses applied to the grid of tube I4. The higher amplitude positive impulses occurring upon disengagement of the movable contact 66 from contact B2 are depicted by reference characters iSii and those occurring when the movable contact is disengaged from contact 64. are indicated by reference characters H32. Similarly, the two groups of negative impulses occurring upon engagement with contacts B4 and t2 are shown by reference characters |84 and |95, respectively.

It should be noted that even though contacts 52 and 54, which are made of very flexible wires, may move somewhat because of the engagement by the movable contact, this has no eiect, electrically speaking, because it is the time of engagement which is controlling and provides the limiting function.

Fig. 8, which depicts vibrations of two different amplitudes, is used to illustrate how the time tube 22 of the amplitude circuit remains conductive, and the current iiow through it, varies inversely with the amplitude of the vibrations. The amplitudes or magnitudes of the vibrations are also directly proportional to the velocities so that the time taken by the movable contact in traveling from one stationary contact to the other, which is inversely proportional to the velocity, is also inversely proportional to the amplitude. Fig. 8 illustrates low and high amplitude vibrations, which are indicated by reference characters i and 25.32, respectively. In the graph the ordinates represent amplitude of vibrations and the abscissae represent time. rIhe time required by the movable contact to move from one stationary contact to the other for a low amplitude vibration is indicated by the reference character L. The time for the movable contact to move between the two stationary contacts for a high amplitude vibration is indicated by the reference character H. inasmuch as the tube 22 is conductive during the time the movable contact is moving between the stationary contacts,l it may be noted from Fig. 8 that the tube is conductive for times varying inversely with the amplitude, i. e., the tube is conductive for a longer period of time for low than it is for high amplitude vibrations. rihe tube 22 has constant current flow characteristics so that the current flow through it also varies inversely with the amplitude.

The operation of the pr'e'sentinvention may be perhaps best reviewed in connection with the balancing of an automobile wheel. The wheel is first provided with a distinctive mark, such as a chalk mark on the tire, which may be readily observed wl'ien the rotating wheel is illuminated by the stroboscopic tube. rIhe control means actuating means is secured to the wheel support, for example, to the axle, by attachment of the permanent magnet thereto'in such manner that the magnet moves vertically as indicated by the arrow alongside it. It should perhaps be observed at this point that the control means 24 and 26 may be built as a single unit which may readily be connected electrically to the remainder of the apparatus including the flasher, frequency, and amplitude circuits, which may be, if desired, constructed as a separate unit and housed within a suitable cabinet or the like.

The wheel is rotated at about the resonant speed and the movable contact 65 centered with switch 86 closed and switch in its indicated position. The centering is effected by adjustment screw 84 which simultaneously moves the stationary contacts 62 and 64 relative to the movable contact 66. The adjustment is properly made when the stroboscopic tube I4 flashes when the chalk mark on the wheel appears at two positions which are 180 degrees apart.

The movable contact |44 is similarly adjusted after it has been connected to the flasher circuit by means of switches lli and |53 which are operated, preferably simultaneously, to their displaced positions whereby control means 2B is connected to the input of flasher tube |4 through conductor |86. The stationary contacts are then adjusted until the chalk mark appears at two positions 180 degrees apart. The switches Il and 153 are then returned to their indicated positions and the apparatus is ready to check the balance of the wheel.

The movable contact |44 may also be centered without connection to the flasher circuit. This is accomplished by observation of the amplitude meter |42 which reads a minimum when the contacts are centered. The minimum reading results from the fact that when the contact is centered, its velocity is the greatest and it moves between the stationary contacts in the shortest time. As a result, the tube 22 is conductive for a minimum length of time and the meter reading, therefore, is a minimum.

In checking the balance of the wheel, the wheel is first brought to a speed above its resonant speed and then decelerated freely to its resonant speed. The resonant speed is indicated by the reading of frequency meter |40. The amplitude meter |42 registers a maximum at resonant speed and thus indicates when resonance has been reached. The switch 85 is opened so that tube hl flashes once for each revolution of 4the wheel, i. e., when the movable contact 66 moves out of engagement with contact 62 which it does when the vibration is vertically upward indicating that the locus of unbalance is at the top at the moment the tube is flashed. The position of the chalk mark, i. e., its apparent stationary angular position, is noted. The whel is then brought to rest with the chalk mark at the noted apparent position. When the wheel is thus positioned, the locus of unbalance is at the top and the wheel may be balanced by adding a weight at the bottom. The weight to be added can be determined from the reading of amplitude meter |42. Thereafter, the wheel may be brought up to its resonant speed, as previously noted on meter |40 and the balance again checked.

The embodiment of the invention illustrated in Fig. 2 is very much like that already described. The primary distinction between the two is that the embodiment of Fig. 2 utilizes a battery 2H] as the source of energy. This battery may supply a relatively high voltage as of about 300 volts across positive and negative power supply lines 2|2 and 2 I4.

The asher and amplifier tubes I4 and 22 are connected across the power supply lines through resistance means. The cathode 90 of tube I4 is connected to the negative line through a cathode bias resistor 2 I 5 (of about 2000 ohms) rlhe anode 98 is connected to the positive power supply line 2 I 2 through the series connected resistors 2 I 8 and 220 (of about 6000 and 4000 ohms, respectively). The latter is shunted by condenser 222 (of about 1000 mf.).

A common potential divider is utilized for al1 three tubes I 4, I8 and 22. It includes the resistors 224, 226, 228, 230 and 232 (of about 500 ohms, 1.5 megohms, 1200 ohms, 4700 ohms and 1500 ohms, respectively). The tube I8 and frequency meter |40 are connected in series across the junctions of resistors 2I8 and 220 and of 224 and 226. The control grid 88 of flasher tube I4 is connected to the junction of resistors 228 and 230 by a series resistor 234 (of about one tenth megohm) The condenser I3!) is connected across the cathode and anode of the tube and the shield grid 94 is connected to the cathode through the resistor 96.

The asher tube grid 88 is coupled to the control means 24 through a condenser 236 (of about .005 mf.) which is connected directly across the grid and the junction of the potential dividing resistors 233 and 240 (of about one tenth megohrn and five tenths megohm, respectively). This junction is also connected to the switch I Il as is the case with the embodiment of the invention illustrated in Fig. 1.

The amplitude circuit tube 22 has its screen grid I'I connected to the junction of resistors 226 and 228. Its cathode I58 is connected by conductor 242 to the junction of resistors 230 and 232, the latter of which acts as a cathode bias resistor for the tube. A by-pass condenser 244 (of about 20 mf.) is connected across conductor 242 and the screen grid ITI). The suppressor grid I I4 is connected to the cathode.

The amplitude meter I 42 is connected in series with resistor 245 (of about .2 megohm) across the anode I 'i8 of tube 22 and the positive line 2I 2. The meter and resistor are shunted by a con denser 248 (of about .4 mf.).

The control grid |50 of the amplitude tube is coupled to the control means 26 through the resistors I52 and I 64 corresponding to the similarly numbered resistors of Fig. 1.

From the foregoing detailed description of the embodiment of Fig. 2 it is apparent that the cir: cuit is substantially like that of Fig. 1 and it is therefore deemed unnecessary to describe its opn1 eration in any detail as it corresponds to that already described.

The apparatus of the present invention is relatively simple compared with other devices in the art, and it provides frequency and amplitude readings and indicates the locus of unbalance so that the wheel may be balanced with a minimum of trouble. Furthermore, the arrangement is such that it can be readily applied to various types of devices and to different wheels of an automobile with a minimum expenditure of time and eifort. It operates satisfactorily over a wide range of amplitudes and frequencies and is, therefore, capable of widespread use.

While two embodiments of the present invention have been described, it should be understood that the details thereof are not intended to be limitative of the invention except insofar as set forth in the accompanying claims.

Having thus described my invention, what I desire to secure by United States Letters Patent is:

1. Balancing apparatus of the type including a gaseous discharge device having a cathode, and anode, and a control grid, including in combination, means including a cathode resistor for connecting the anode-cathode circuit to a source of power, means including a potential divider connected with a potential source and a resistor connecting the divider to said grid for applying a voltage to the grid, means including a second p0- tential divider connected with a source of potential, a condenser connecting the grid to the second potential divider and circuit controlling means coupled to said condenser and said second mentioned potential divider controlling the eil`ectiveness of a portion of said voltage divider for producing control impulses transmitted to the grid through said condenser for controlling the conductivity of said device, and means connected to said circuit controlling means and adapted to be connected to a body to be tested for unbalance.

2. Balancing apparatus of the type including a gaseous discharge device having a cathode, an anode, and a control grid, including in combina tion, means including a cathode resistor for connecting the anode-cathode circuit to a potential source, means including a potential divider connected across the potential source and a resistor connecting an intermediate portion of the divider to said grid for applying a voltage to the grid, and means including a second potential divider connected across the potential source, a condenser connecting the grid to an intermediate portion of the second potential divider for supplying control impulses to the grid, and mechanical switch means operated alternately to short circuit the portion of the second voltage divider between said condenser and the negative side of the potential source for producing control impulses transmitted to the grid through said condenser for controlling the conductivity of said device, and means connected to said switch means and adapted mechanically to be connected to a body to be tested for unbalance.

3. Balancing apparatus of the type including a gaseous discharge device having a cathode, an anode, and a control grid, including in combination, means including a cathode resistor for connecting the anode-cathode circuit to a source of power, means including a potential divider coupled with a potential source and a resistor connecting the divider to said grid for applying a voltage to the grid, means including a second potential divider connected with a source of potential and a condenser connecting the grid to the second potential divider for supplying control impulses to the grid, means including circuit controlling means coupled to said second mentioned potential divider for controlling the effectiveness of a portion of said voltage divider for producing control impulses transmitted to the grid through said condenser for controlling the conductivity of said device, a second condenser connected across said discharge device, a resistor connected between the anode and the positive side of said potential source, a third condenser parallel to the last mentioned resistor, and means including a rectifier and a meter also connected across said last mentioned resistor for measuring the average voltage across said third condenser, and means connected to said circuit controlling means and adapted to be connected to a body to be tested for unbalance.

4. Control mechanism for balancing apparatus', including in combination, afpair-of'exible contacts spaced apartf a short distance, 'amovable contact, andresilientfmeansfor supporting said movable contact for movement between and into and out off'engagement'with thelpair of contacts, said lastmentioned means-including a first resilientl reed havingv tliefend" opposite the contact carryingV endlsecuredto1a1stationary support, a secondfresilient reeda'djacentv said i'irst mentioned reed having a'permanentmagnet secured at itsl free end, saidI reedsA d'ening a configuration correspondingA generally to' a Gothic arch with the-movable-contactlocatedat its=apeX;

5. In a balancing'apparatuslfrdetecting'the unbalance oi a rotating body carried by a supportyieldably mounted upon-'a base to permit vibrations oi' the body and: the1 supportK having a substantial amplitude; a control' mechanism comprising iirstv and second contacts, means securing thecontacts to the baseA with aspace between the two contacts, a third' movable con"- tact, an operating member adaptedto be rigidly connected with the support' and thusv to vibrate with the support, yieldable means securing the movable contact to thev operating member and positioning the movable contact. to occupy a central portion of thespace between said rst and second' contacts, the: remainder.v of: the space being muchA shorterY Athan the amplitude of the vibrations of the. support, whereby the movable contactv is movable, between the. first and second contacts in a. brief timel interval substantially when the displacement ofzthezvibrating'support is zero.

6. Apparatus for ing a stroboscopebalancing aY body, comprisincluding an electron tube having a grid; a source of grid potential; and control means for varying the potential of the grid to flash the stroboscope, said control means including a pair of stationary'conta'cts, a movable contact operable into and voutY of engagement with said'stationary'cont'acts, said movable contact being electrically coupled with the source and adapted to be mechanically coupled with the body, means coupling one of the-stationarycontacts to the grid, andmanually operable switch means for selectively coupling and uncoupling the other of saidstationary contacts to said grid, whereby said stroboscope mayr be dashed once or twice for each cyclic movement of the body as desired.

'1. Apparatus for balancing avibrating body, comprisinga pair of electron tubeshaving respective grids, one of said tubes being'a stroboscopc tube; and control means for varying the potentials of the grids, said control. means including two pairs of adjustably mounted contacts, two movable contacts respectively` operable into and out of engagementI with said adjustably. mounted contacts, common means adapted mechanically to connect the movable contactsiwith the body to operate the movable 'contacts in synchronism withvibrations of the. body, a first manually operable switch selectively to couple one of said pairs of adjustably mounted contacts with either of said electron tubes, a second manually operable switch selectively to couple said one or the other ofi said pairs off adjustably mounted contacts with tlie stroboscopic tube, and circuit meanstoconnect saidswitches in series when both said switches are moved to such position as to couple said one pair of adjustably mounted contacts to the stroboscopic tube, whereby either oi said pairs of adjustably 14 mounted contacts' may be centeredwitharespect to said movable contactsby meansV of thestroboscopic tube.

8. Apparatus for indicating the locus of'unbalance of a body rotatably mounted upon a; yieldable support and for indicatingv the amplitude of the vibrations `of the body, comprising a stroboscopic tube, an amplitude indicator including a second tube, av frequency indicator'including a third tube, means coupling'said third tube with said stroboscopic' tube; al pair; oimeans operable to supply control impulsesinresponse to vibrations, each ofsaid: means being, adjustable to supply said impulsesf when the instantaneous vibrational displacement oi said body is substantially zero, a single means adapted mechanically to connect saidpair of control meansY with the support, a rstf manually oper.- able; switch adapted selectively to; couple said stroboscopic tube withV either; of said control means, a second manually'operableswitch selectively to couple one oi saidcontrol meansvwith eitherfsaidcsecond tubeor with the stroboscopic tube, and circuit means to, connect said switches in series when both switches are-,moved tosuch position as to couple said one control means to the stroboscopic tube, whereby either of. said control means may lie-adjusted to supply impulses when'the instantaneous vibrational displacement of the support is substantially zero during an adjustment phase ofoperationof the apparatus and said stroboscopic tube and said second tube may be supplied with'such impulses during a normal operating phase oi opera-tions;

9. In an apparatus for indicating the unbalance ofy a rotating body carried by a yieldable support, a control mechanism comprising' a stationary member, av pair of' flexible contacts securedlto the stationary member, and spaced apart a short` distance, iirstand second substantially parallel. elongated reeds, amovablef contact secured to the'outer end of said iirst and second reeds for movement in a plane substantially perpendicular; to the reeds between and into and out of engagement with, the pair;v of contacts, the inner end of the first reed being, securedlto the stationary member, actuating means adapted to be connected with the support for movement inv response to vibrations of thesupport, the inner end ofthe second reed beingVv connected with the said actuating meansfor longitudinal vibrational movement of the second reed, whereby the vibrations of the support are amplified and move the-movable contact between the flexible contact and a stationary contact in a brief interval relative to the period of the vibration oi the support.

10. Apparatus for indicating the unbalance of a rotating body, comprisingv a stroboscopic device, an actuating means adapted to. be mechanically coupled with the body for movement in response to vibrations of the body, a stationary. support, a switchincluding a pairI oiV flexible contacts `secured to the support and spacedapart a short distance, iirst and secondsubstantially parallel flat elongated resilient membersv spaced apart a short distance, a movable contact secured to the outer end oi" said rst andisecond members for movement substantially perpendicular tov said members between and into and out of engagement with said flexiblecontacts, the inner end ci the first member being connected with the stationary support and the inner end of the second member being connected with the actuating means for longitudinal vibrational displacement of the second member, and means electrically coupling the flexible contact and the movable contacts with the stroboscopic device for flashing the device upon operation of the switch.

11. An apparatus for measuring the frequency of electrical impulses, comprising a gaseous discharge device including a grid, an anode and a cathode; grid circuit means adapted to impress the impulses upon the grid to initiate conduction in the device periodically in unison with the impulses; a capacitor connected between the anode and the cathode to provide abrupt surges through the device; a potential source for charging the capacitor including means including a high voltage terminal to provide a relatively high voltage and means including a lower voltage terminal to provide a relatively lower voltage; means to connect the potential source to the device including irst and second charging impedances connected in series between the high voltage terminal and the anode, the first charging impedance having rst and second terminals, the first terminal being connected to the high voltage terminal; and means to measure the f average charging current supplied by the potential source to the capacitor, including a current measuring instrument and a rectifier connected in series between the low voltage terminal and the second terminal of the first charging impedance, the rectier being polarized to prevent current flow from the second terminal of the first charging impedance to the low voltage terminal.

12. Balancing apparatus for indicating the amplitude of the vibrations of a body, comprising a switch operating member adapted to be con nected with the body for vibration in unison therewith through a stroke proportional to the amplitude of the vibrations of the body, an electrical switch connected with the member for operation when the member traverses a segment of its stroke, the segment being substantially fixed in length, the switch including means providing for substantial overtravel of the member outside the segment, the switch being closed during overtravel, vibrational amplitude indicating means including an indicator of the average value of an electric current, and electrical circuit means coupling the switch to the indicating means to supply current having a predetermined value to the indicator when the switch is open, the 'current supplied to the indicator being changed by a predetermined amount when the switch is closed.

13. Balancing apparatus for indicating the amplitude of the vibrations of a body throughout a predetermined range of vibrational displacement, comprising a switch including a pair of contacts spaced apart a predetermined amount, a third contact positioned between the pair of contacts, stationary means supporting said pair of contacts, a switch operating member connected to said third contact and adapted to be connected with the body and movable through a predetermined distance for moving the third contact relatively to shift the third contact between the contacts of the pair, the last mentioned distance being substantially less than the range of vibrational displacement of the body, means in the switch providing for substantial overtravel of the switch member beyond said predetermined distance, means electrically connecting the contacts of the pair together, circuit means connected between the contacts of the pair and the third contact to produce impulses in accordance with opening of the switch, and means coupled to the circuit for measuring the duration of the impulses in proportion to the interval beween their occurrences.

14. Balancing apparatus for indicating the amplitude of the vibrations of a body throughout a predetermined range of Vibrational displacement, comprising a switch including a pair of contacts spaced apart a predetermined amount, a third contact positioned between the pair of contacts, stationary means supporting said pair of contacts, a switch operating member connected to said third contact and adapted to be connected with the body and movable through a predetermined distance for moving the third contact relatively to shift the third `Contact between the contacts ci" the pair, the last men* tioned disance being substantially less than the range of vibrational displaceemnt oi the body, means in the switch providing for substantial overtravel of the switch operating member beyond said predetermined distance, and means electrically connecting the contacts of the pair together; an electron tube having a grid, an anode and a, cathode; a source of potential; a grid-cathode circuit including the source, the switch and the grid for connecting and disconnecting the source and the grid when the switch is closed and opened; and an anode-cathode circuit including an average anode current indicator for indicating the amplitude of the vibrations.

JOSEPH O. MESA.

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